Grip force and force sharing in two different manipulation tasks with bottles

Abstract

Grip force and force sharing during two activities of daily living were analysed experimentally in 10 right-handed subjects. Four different bottles, filled to two different levels, were manipulated for two tasks: transporting and pouring. Each test subject’s hand was instrumented with eight thin wearable force sensors. The grip force and force sharing were significantly different for each bottle model. Increasing the filling level resulted in an increase in grip force, but the ratio of grip force to load force was higher for lighter loads. The task influenced the force sharing but not the mean grip force. The contributions of the thumb and ring finger were higher in the pouring task, whereas the contributions of the palm and the index finger were higher in the transport task. Mean force sharing among fingers was 30% for index, 29% for middle, 22% for ring and 19% for little finger.

Practitioner Summary: We analysed grip force and force sharing in two manipulation tasks with bottles: transporting and pouring. The objective was to understand the effects of the bottle features, filling level and task on the contribution of different areas of the hand to the grip force. Force sharing was different for each task and the bottles features affected to both grip force and force sharing.     

The effect of tool handle shape on hand muscle load and pinch force in a simulated dental scaling task

Work-related upper extremity musculoskeletal disorders, including carpal tunnel syndrome, are prevalent among dentists and dental hygienists. An important risk factor for developing these disorders is forceful pinching which occurs during periodontal work such as dental scaling. Ergonomically designed dental scaling instruments may help reduce the prevalence of carpal tunnel syndrome among dental practitioners. In this study, eight custom-designed dental scaling instruments with different handle shapes were used by 24 dentists and dental hygienists to perform a simulated tooth scaling task. The muscle activity of two extensors and two flexors in the forearm was recorded with electromyography while thumb pinch force was measured by pressure sensors. The results demonstrated that the instrument handle with a tapered, round shape and a 10 mm diameter required the least muscle load and pinch force when performing simulated periodontal work. The results from this study can guide dentists and dental hygienists in selection of dental scaling instruments.     

A survey of the optimal handle position for boxes with different sizes and manual handling positions

Handles on objects are very important for enhancing the safety and efficiency of manual handling for people who use them. In this study, four different prototype boxes with auxiliary handles were designed to determine the optimal handle position of a box based on the evaluated user preferences and body part discomfort (BPD). Twenty male students participated in the experiment. Likert-5 point summated rating was applied to evaluate user preferences for the provided boxes with handles in upper, middle, and lower positions, in four different sizes and manual handling positions. Ten additional subjects were asked to indicate their BPD on a body chart after performing a similar experiment. The results show that the subjects preferred the upper part of the handle on a small box regardless of handling position; while the mid to upper parts of the handle on a big box were preferred for handling above the waist height. BPD also indicated that an upper handle was less stressful for a relatively smaller box than a big one; and mid to upper handles were less comfortable for a big box. The optimal handle positions depending on box size and handling position were suggested based on the results of the evaluation. It is thus recommended that a box provides a handle according to its relevant position, depending on size and manual handling condition, to reduce the musculoskeletal stress and in turn to increase user satisfaction.     

Comparison of measurement methods for quantifying hand force

Hand force is a known risk factor for upper extremity disorders. The objective of the present study was to determine the characteristics of, and the relationships between, exposure assessment methods to quantify hand force. Five methods, used in the laboratory or the field, were used to quantify hand force at three force magnitudes: two direct (or technical) measurement methods, force transducers and electromyography; an observational method; and two self-report approaches, force matching and a visual analogue scale. Five tasks, simulating manual work activities, were performed by 20 participants. The coefficients of variation of measures within and between participants were moderate. All approaches clearly distinguished between the three force levels tested. The reliability of the methods ranged from poor (observation method without information) to good (force transducers method and observation method with information). The measurement methods correlated moderately over all five tasks. Predictions of grip force across all five tasks were poor and even for single tasks the predictions were not much better. The tasks in this study were still simplified; in the field tasks are even more complex and the measurement characteristics might be expected to be less good. A hand force exposure assessment method should therefore be calibrated and tested for each type of hand activity before use.     

Comparison of measurement methods for quantifying hand force

Hand force is a known risk factor for upper extremity disorders. The objective of the present study was to determine the characteristics of, and the relationships between, exposure assessment methods to quantify hand force. Five methods, used in the laboratory or the field, were used to quantify hand force at three force magnitudes: two direct (or technical) measurement methods, force transducers and electromyography; an observational method; and two self-report approaches, force matching and a visual analogue scale. Five tasks, simulating manual work activities, were performed by 20 participants. The coefficients of variation of measures within and between participants were moderate. All approaches clearly distinguished between the three force levels tested. The reliability of the methods ranged from poor (observation method without information) to good (force transducers method and observation method with information). The measurement methods correlated moderately over all five tasks. Predictions of grip force across all five tasks were poor and even for single tasks the predictions were not much better. The tasks in this study were still simplified; in the field tasks are even more complex and the measurement characteristics might be expected to be less good. A hand force exposure assessment method should therefore be calibrated and tested for each type of hand activity before use.     

Performance in gripping and turning -a study in hand/handle effectiveness

The biomechanics of the hand/handle linkage were studied to generate data for the optimal design of screwdrivers and other devices which are gripped and used forcefully against resistance. Comparisons were made between smooth and rough steel cylinders and a range of commercially available screwdrivers of varying size, shape and surface quality. None of the screwdrivers was significantly better for the exertion of torque than rough cylinders of the same mean diameter, nor was any worse than a comparable smooth cylinder. It is therefore concluded that for forceful activity the precise shape of the handle is unimportant, the effectiveness of the activity being limited by the size of the handle and the quality of the hand/handle interface.     

水下灵巧手指端力传感器及静态标定方法

指端力传感器是水下灵巧手实现复杂作业的关键,开展了基于圆筒结构的指端力传感器研究。由于指端力传感器的结构特点,采用通常六维力静态标定方法较困难,且精度无法保证。因此,提出基于径向基函数(RBF)神经网络的静态标定方法,对标定装置、标定过程设计进行了研究。以研制的指端力传感器为对象进行了静态标定试验。结果表明:使用基于RBF神经网络的静态标定方法有效地保证了传感器测试精度,可满足目前水下灵巧手研究要求。结果证明了该方法的可行性和有效性。     

Variability and misclassification of worker estimated hand force

Ergonomic studies often use worker estimated hand force reproduced on a dynamometer to quantify force exposures but this method has not been well-studied in real work settings. This study evaluated the validity of worker estimates of hand force in a field study and determined the misclassification of worker estimated hand force exposures compared to directly measured forces. Eight experienced sheet metal assemblers completed ¼-inch diameter fastener installations using 6 different pneumatic tools. Grip forces were recorded by a pressure mat and were compared to worker estimated forces demonstrated on a dynamometer. Directly measured and worker estimated readings showed moderate correlations (0.53–0.67) for four installation tools and fair to moderate for two tools. The coefficient for variation of force estimates was 65% within repeated subject trials and 78% between averaged subject trials but 69% between subject trials during actual tool installations. Misclassification of worker estimated exposures varied by two cut-points: 29% using 4.0 kg and 49% using 6.0 kg. The force match procedure may provide adequate differentiation of high and low exposures in some settings, but is likely to result in substantial misclassification in other settings.     

A force method for calculating time varying stresses in concrete structures

A method for the linear time varying stresses of concrete structures at elevated temperature is presented. The method described is of a one-step direct formulation technique based on the principle of variational calculus.The analytical procedure of the variational principle is briefly described and the equations for the uniaxial state of stress are developed.The application of the method is described and the solution is carried out by a finite element stiffness analysis for two different types of stress distribution and a set of self equilibrating stress distribution. Predicted stresses by the proposed method are compared with other analytical methods based on a step-by-step analysis.     

Assessment of grip force and subjective hand force exertion under handedness and postural conditions

The Borg CR-10 scale has been used to quantify the perception of physical exertion. An experiment was conducted to test the grip force of males on four levels of the CR-10 scale under experimental conditions. It was found that the subjects applied higher grip forces than they perceived at levels 2, 5, and 7 on the scale. The grip forces between dominant and non-dominant hands at low CR-10 levels were negligible. The grip forces were significantly different between the two hands at level 10. Similar results were found for the postural conditions. A follow-up experiment was conducted to estimate the subjective rating when applying a pre-determined grip force under the same conditions. Regression models were established to link the relationship between the subjective rating and hand force. The estimated ratings were lower than those actual values under all the tested conditions, even though the models have high R² values.     

The natural angle between the hand and handle and the effect of handle orientation on wrist radial/ulnar deviation during maximal push exertions

The purpose of this experiment was to quantify the natural angle between the hand and a handle, and to investigate three design factors: handle rotation, handle tilt and between-handle width on the natural angle as well as resultant wrist radial/ulnar deviation (‘RUD’) for pushing tasks. Photographs taken of the right upper limb of 31 participants (14 women and 17 men) performing maximal seated push exertions on different handles were analysed. Natural hand/handle angle and RUD were assessed. It was found that all of the three design factors significantly affected natural handle angle and wrist RUD, but participant gender did not. The natural angle between the hand and the cylindrical handle was 65 ± 7°. Wrist deviation was reduced for handles that were rotated 0° (horizontal) and at the narrow width (31 cm). Handles that were tilted forward 15° reduced radial deviation consistently (12–13°) across handle conditions.

Practitioner summary: Manual materials handling (MMH) tasks involving pushing have been related to increased risk of musculoskeletal injury. This study shows that handle orientation influences hand and wrist posture during pushing, and suggests that the design of push handles on carts and other MMH aids can be improved by adjusting their orientation to fit the natural interface between the hand and handle.     

Evaluation of a curved handle and handle positions for manual materials handling

Abstract

Previous studies of handles for two-handed box handling have shown that the best angle for a handle on a box varies with height above the floor. In order to minimize the accommodation between handle and wrist required at different heights, a curved handle was proposed. Six manual materials handling workers lifted 9 kg and 13 kg boxes between conveyors at floor and waist heights for three minutes while body angles were analysed from video tape recordings. Two symmetric and two asymmetric handle positions were tested. Both straight and curved handles resulted in excellent hand/handle fit but were not significantly different from each other on any measures.     

Characterizing human hand prehensile strength by force and moment wrench

Characterizing human hand capabilities or demand created by various occupational tasks or activities of daily living has been mainly accomplished by measuring the maximum force exerted on a force dynamometer in a number of standard grips, for example power, key pinch and tip pinch grips. A framework is proposed instead to characterize human hand prehensile strength in generic form by describing external force and moment wrench capability, where a wrench is a vector describing the forces and moments applied at a point. It is further suggested that if tools and activities are characterized by the internal forces and external forces and moments required, a better understanding of the human prehension in occupational settings and during activities of daily living can be obtained. An example of using a pistol grip drill is used to show the utility of the approach.     

Characterizing human hand prehensile strength by force and moment wrench

Characterizing human hand capabilities or demand created by various occupational tasks or activities of daily living has been mainly accomplished by measuring the maximum force exerted on a force dynamometer in a number of standard grips, for example power, key pinch and tip pinch grips. A framework is proposed instead to characterize human hand prehensile strength in generic form by describing external force and moment wrench capability, where a wrench is a vector describing the forces and moments applied at a point. It is further suggested that if tools and activities are characterized by the internal forces and external forces and moments required, a better understanding of the human prehension in occupational settings and during activities of daily living can be obtained. An example of using a pistol grip drill is used to show the utility of the approach.     

A new method for estimating hand internal loads from external force measurements

This study examines using force vectors measured using a directional strain gauge grip dynamometer for estimating finger flexor tendon tension. Fifty-three right-handed participants (25 males and 28 females) grasped varying-sized instrumented cylinders (2.54, 3.81, 5.08, 6.35 and 7.62 cm diameter) using a maximal voluntary power grip. The grip force vector magnitude and direction, referenced to the third metacarpal, was resolved by taking two orthogonal grip force measurements. A simple biomechanical model incorporating the flexor tendons was used to estimate long finger tendon tension during power grip. The flexor digitorum superficialis and the flexor digitorum profundus were assumed to create a moment about the metacarpal phalange (MCP) joint that equals and counteracts a moment around the MCP joint measured externally by the dynamometer. The model revealed that tendon tension increased by 130% from the smallest size handle to the largest, even though grip force magnitude decreased 36% for the same handles. The study demonstrates that grip force vectors may be useful for estimating internal hand forces.     

A new method for estimating hand internal loads from external force measurements

This study examines using force vectors measured using a directional strain gauge grip dynamometer for estimating finger flexor tendon tension. Fifty-three right-handed participants (25 males and 28 females) grasped varying-sized instrumented cylinders (2.54, 3.81, 5.08, 6.35 and 7.62 cm diameter) using a maximal voluntary power grip. The grip force vector magnitude and direction, referenced to the third metacarpal, was resolved by taking two orthogonal grip force measurements. A simple biomechanical model incorporating the flexor tendons was used to estimate long finger tendon tension during power grip. The flexor digitorum superficialis and the flexor digitorum profundus were assumed to create a moment about the metacarpal phalange (MCP) joint that equals and counteracts a moment around the MCP joint measured externally by the dynamometer. The model revealed that tendon tension increased by 130% from the smallest size handle to the largest, even though grip force magnitude decreased 36% for the same handles. The study demonstrates that grip force vectors may be useful for estimating internal hand forces.     

The effect of handle friction and inward or outward torque on maximum axial push force

OBJECTIVE: To investigate the relationship among friction, applied torque, and axial push force on cylindrical handles. BACKGROUND: We have earlier demonstrated that participants can exert greater contact force and torque in an "inward" movement of the hand about the long axis of a gripped cylinder (wrist flexion/forearm supination) than they can in an "outward" hand movement. METHOD: Twelve healthy participants exerted anteriorly directed maximum push forces along the long axis of aluminum and rubber handles while applying deliberate inward or outward torques, no torque (straight), and an unspecified (preferred) torque. RESULTS: Axial push force was 12% greater for the rubber handle than for the aluminum handle. Participants exerted mean torques of 1.1, 0.3, 2.5, and -2.0 Nm and axial push forces of 94, 85, 75, and 65 N for the preferred, straight, inward, and outward trials, respectively. Left to decide for themselves, participants tended to apply inward torques, which were associated with increased axial push forces. CONCLUSION: Axial push force was limited by hand-handle coupling--not the whole body's push strength. Participants appeared to intuitively know that the application of an inward torque would improve their maximum axial push force. Axial push forces were least when a deliberate torque was requested, probably because high levels of torque exertions interfered with the push. APPLICATION: A low-friction handle decreases maximum axial push force. It should be anticipated that people will apply inward torque during maximum axial push.     

Kinematic analysis and position/force control of the Anthrobotdextrous hand

The increasing demand for robotic applications in unstructured environments is motivating the need for dextrous end-effecters which can cope with the wide variety of tasks and objects encountered in these environments. A new anthropomorphic robot hand (Anthrobot) which was designed for these environments is described. In this paper the problem of developing the kinematics and unit consistent hybrid position/force control of the Anthrobot fingers is considered as the first step toward its utilization for either teleoperation or autonomous operation. A dynamic model of the fingers is identified and used to develop the control laws. The experimental results of applying the control to the Anthrobot are discussed.     

Effect of elliptic handle shape on grasping strategies, grip force distribution, and twisting ability

A generic torque model for various handle shapes has been developed and evaluated using experimental data. Twelve subjects performed maximum isometric torques using circular and elliptic cylinders in medium and large sizes (circular: r = 25.4, 38.1 mm; elliptic: semi-major/minor axes = 30.9/19.3, 47.1/27.8 mm) finished with aluminium and rubber, in two opposite directions. Torque, grip force distribution, and finger position were recorded. Maximum torques were 25%, 7%, and 31% greater for the elliptic, large-size, and rubber-finished cylinders than for the circular, medium-size, and aluminium-finished cylinders, respectively. Greater torque for the elliptic cylinders was associated with 58% greater normal force that the subjects could generate for the elliptic than circular cylinders. The model suggests that greater torques for the large-size and rubber cylinders are related to long moment arms and greater frictional coupling at the hand-cylinder interface, respectively. Subjects positioned their hands differently depending on torque direction to maximise their normal force and torque generation. STATEMENT OF RELEVANCE: Desirable handle features for torque generation may be different from those for grip only. Design of handles per advantageous handle features (e.g., shape, size, and surface) may help increase people's torque strength and contribute to increased physical capacity of people.